NZXT used the Seasonic Focus platform, only this time, it left out the digital circuits of the E series to allow for a lower price. And that is what matters the most for the majority of people. Currently, the NZXT E650 is almost $45 more expensive than the C650, with the significant differences being the digital voltage, and temperature monitoring capabilities of the former. You can read more about this in our review of the E850. If you want to keep things simple and save some bucks, the C650 is a better choice than the E650 since both are based on the same platform.
The overall performance that the C650 is pretty good, but it cannot beat the Corsair RM650x and the XPG Core Reactor with similar capacity, which uses CWT platforms. The EVGA SuperNOVA 650 G3 remains the best performer in this category. Still, the whole G3 line will be phased soon by the notably inferior G5 line so that EVGA won't be in the club anymore (in this category, at least). All in all, the NZXT C650 is a good choice if you want a reliable PSU with good performance and silent operation. Its major flaw is the single EPS connector, which restricts its usability with mainboards requiring more power in the CPU area. At the moment, there aren't many PSUs in this price range and Wattage offering two EPS connectors, with the XPG Core Reactor 650, Corsair RM650, and the Asus Rog Strix 650 being the best choices, should you need a pair of EPS connectors.
MORE: Best Power Supplies
MORE: All Power Supply Content
Disclaimer: Aris Mpitziopoulos is Tom's Hardware's PSU reviewer. He is also the Chief Testing Engineer of Cybenetics and developed the Cybenetics certification methodologies apart from his role on Tom's Hardware. Neither Tom's Hardware nor its parent company, Future PLC, are financially involved with Cybenetics. Aris does not perform the actual certifications for Cybenetics.